This invention relates to preparation of uranium tetrafluoride (UF.sub.4) in a wet process, and more particularly to a process and an apparatus for continuous preparation of uranium tetrafluoride hydrate with coarse particle size.
The known wet process for preparing uranium tertrafluoride is batchwise, which generally comprises the following steps: electrolytically reducing an uranyl chloride solution (UO.sub.2 Cl.sub.2) obtained in a solvent extraction step into an uranous chloride solution (UCl.sub.4), charging the uranous solution into a reaction tank, adding hydrofluoric acid of 50% concentration in the tank to produce and precipitate uranium tetrafluoride hydrate (UF.sub.4 .multidot. nH.sub.2 O), then filtering, washing and drying the thus precipitated uranium tetrafluoride hydrate, and then heating the hydrate by passing nitrogen gas therethrough to remove water of crystallization to thereby obtain anhydrous tertraflouride (UF.sub.4).
However, uranium tetrafluoride hydrate from such batch type precipitation method is so small in particle size, which is usually of about 1 to 10.mu., that the filtration efficiency is poor. Low efficiency is also unavoidable in the dehydration step and in the conversion step to uranium hexafluoride (UF.sub.6) as hereinbelow described, resulting in undesirable pysical properties of the product.
In case of producing metallic uranium by adding magnesium powder to uranium tetraflouride and then heating and fusing the mixture, no impediment is caused even if the uranium tetrafluoride used is of extremely fine particle size. On the other hand, in production of enriched uranium which is currently the main source of nuclear fuel, it is necessary to charge uranium tetrafluoride into a fluidized bed type reaction tower and then to feed preheated fluorine gas into the bottom of the tower to thereby reduce uranium tetrafluoride to hexafluoride (UF.sub.6). At this time, if the crystal particles of uranium tetrafluoride are extremely fine, the passage of the fluorine gas is somewhat retarded due to poor fluidity of the particles. In such case, a part of fluorine gas is caused to pass through the tower without undergoing any reaction, resulting in non-uniform reaction and poor utilization of the fluorine gas.